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Rerouting hot water radiator piping

jsmit
jsmit Member Posts: 4
I am finishing out a room in my attic, and would like to move some of the existing hot water piping out of the way.  The heating system is cast iron radiators, which are original to the house from 1923.  I've been doing some reading, including Dan's book 'Classic Hydronics', and figured out that the heating system was originally an overhead gravity system, which has since had a circulator added to it.  The main supply line is a 2-1/4" pipe which rises from the cellar to the attic and runs along the ridge, then turns back downstairs in the area I'm working in.  Can the main line be rerouted without affecting the flow through the pipe?  There are a couple of options for routing the pipe, one would add 1 turn to the existing setup, and the other would add 4.

I would also like to install an additional radiator in the new room.  The overall size of the room is 13'x17'. I have a couple of spare radiators, one 4 section, and one 8 section.  I was thinking of installing one of them near the new piping and tying the supply side into the rerouted main line, and running the return back down to the cellar and tying it into the main return line. A couple other smaller radiators in the house are connected with 1" or 1-1/4" pipe.  I assume the same size would work for the new radiator? 

I'd appreciate any thoughts or comment anyone might have to help.  I've attached a photo of the existing pipe and how I was thinking of rerouting it.

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 17,043
    edited February 2012
    Rerouting

    shouldn't cause any problems at all, although I would stay with the pipe sizes as changing size would affect head loss, and could mess up the balance of the system.



    Adding a radiator, however, is another matter.  Water -- almost as much so as steam -- is unvbelievably lazy, and will take whatever path offers the least resistance.  Unless the new radiator is very carefully thought out, and you provide balancing valves on both the new radiator and the old line, you may find that one or the other gets all the flow.  Balancing this sort of thing can be very tricky.  In fact, if you found that you had to throttle the existing radiator to get heat into the new one, you might well find that the balance of the rest of the house was thrown off!



    I'm sort of assuming that there is a manifold arrangement of some sort in the basement with controls on it?  If so, it might be better to add the new radiator as a separate zone entirely.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • jsmit
    jsmit Member Posts: 4
    There isn't any type of manifold on the system

    It's all pretty much the original piping with the 2-1/4" main coming off the boiler, branching off to separate radiators, and then connecting back to the 2-1/4" pipe returning to the boiler, all on one zone.  At some point, another bathroom was added upstairs, and they added a new radiator in there.  A 1" pipe comes off a T in the main line to feed the radiator, and another 1" line returns down to the cellar and ties into the main return line just prior to the boiler.  I was thinking of doing something similar for the radiator I'd like to add.  I know these systems used special types of diverter T's to direct the water.  I'm not sure if mine uses any of these, because they are either buried in the wall, or covered with the original asbestos insulation, which I haven't messed with.  Would it be ok to just use a standard T fitting with a 1" or 1-1/4" pipe feeding the new radiator?

    There are only two more radiators beyond the point where the new one would go.  One of them is in a large one in a bedroom that currently gets a bit warmer than the rest of the house, so it wouldn't be bad if the new one reduced the flow to that radiator a little. 

    If I run a return line from the new radiator down to the cellar, would it be better to tie it directly into the main return line, or run it back to the boiler and tie it in closer to there?  It's about another 20' further to go back to the boiler.  I guess a valve could be added to where it ties back into the main return to adjust the flow as necessary?  The new return could be done with PEX, couldn't it?
  • Jamie Hall
    Jamie Hall Member Posts: 17,043
    Worth a try...

    that is a classic description of a gravity fed system!  The thing with those is that the head losses in the pipes -- because they were so big -- are very small.  I'm not an expert in those systems by any means, so take what I say with some caution, but I suspect you could do it as you are suggesting.  The return could be PEX, but to keep the head loss down I'd use rather large PEX -- perhaps 1".  But I would regard the whole thing as an experiment, and I'd want the valves... just in case.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • jsmit
    jsmit Member Posts: 4
    edited February 2012
    Schematic Drawing

    Here is a drawing I did showing the layout of the existing system, plus the changes I'm thinking of.  I was thinking of using 1" pex as a minimum for the new radiator, or possibly 1-1/4" if needed.  I'll keep the main line the same size as the existing pipe.
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